In mobile radio communications networks, such as cellular telephone systems, neighboring radio cells provide coverage of the area to be serviced. Each cell has a base station (BS) operating on a set of radio channels. A group of base stations is controlled by a mobile switching center (MSC) which controls calls to and from the public switched telephone network (PSTN), integrated services digital network (ISDN), and public land mobile network (PLMN). The MSC typically handles switching, routing, and charging for calls.
It is desirable to provide mobile subscribers with supplementary services that typically require an individual subscription before that service can be invoked. One system in which such supplementary services may be provided is the Global System for Mobile communications (GSM). See for example, GSM technical specification 03.78, version 5.0.0, relating to Customized Applications for Mobile network Enhanced Logic (CAMEL) published by the European Telecommunications Standards Institute (ETSI).
Individual supplementary subscriber services may be divided into two types: those which modify or supplement the process of an originating call (referred to here as "A-subscriber services"), and those which modify or supplement the process of terminating (i.e., receiving) a call, (referred to here as "B-subscriber services"). The present invention is particularly concerned with B-subscriber services where call-related information is provided to the B-subscriber's mobile. One such call-related parameter is the telephone number or other identification of the calling party and is sometimes referred to as calling line identification presentation (CLIP).
While automatic number identification (ANI) services are known in fixed telephony networks, mobile telephony networks present unique challenges to reliably providing such identification to roaming mobile subscribers. In fact, to place a call which terminates at a mobile station whose location may be continually changing, plural databases are required in the mobile communications network for keeping track of mobile stations. For example, many mobile communications networks such as GSM employ a home location register (HLR) database node. The HLR stores the subscriptions of various mobile subscribers as well as the location of the mobile station. In particular, the HLR stores information that identifies the mobile switching center currently serving the present location of the mobile station. This information is updated as the mobile station moves around by having the mobile station register its location with the HLR by means of a mobile switching center (MSC). More specifically, when a mobile station roams into a new mobile switching center area, it registers with that new MSC, and the MSC requests data about the mobile station from the HLR. At the same time, the HLR is informed in which MSC area the mobile station is presently located. Consequently, when the mobile station places a call, the MSC already has the information necessary for call set-up without having to interrogate the HLR.
Also employed in monitoring the location of mobile stations is a visitor location register (VLR) which is associated (and normally co-located) with each MSC. The VLR contains temporary subscriber information needed by the MSC to provide service for visiting subscribers and can be seen as a "distributed" HLR. When a mobile station roams into a new MSC service area, the VLR associated with that MSC requests data about the mobile station from the HLR and stores it. In short, the VLR is used to service roaming mobile stations.
When a call is set up from an initial or gateway mobile switching, center where a mobile-destined call enters the mobile network, to the serving MSC/VLR, the calling party's number may not be provided or otherwise readily accessible. For example, when the called mobile subscriber is roaming in a visiting mobile network, it is often the case that the transit network carrying the call to the visited network either will not or cannot provide calling party information. There are also interconnect agreements between various communications carriers that do not include the transfer of calling party numbers.
There is an additional problem in that there is currently no provision for combining a calling party identification service within a virtual private network (VPN) private numbering plan. In particular, a private number associated with a mobile station in accordance with a VPN numbering plan (rather than a conventional length/formatted telephone number) is not transferred to the mobile switching center where the mobile subscriber is currently registered as part of the call set-up message information provided for a particular call. This problem is further exacerbated when VPN services extend across cellular provider networks or across international boundaries as described above.